There is an increasing demand for accurate, yet low-cost and highly reliable guidance, control and navigation systems for air, land, sea and space vehicles. Many of these navigation systems employ gyroscope devices, which can precisely measure changes in orientation (e.g., pitch, roll, yaw) of the vehicles as the vehicles move. In many applications, the well known mechanical gyroscope with its rotating wheels has been replaced by the laser gyroscope. Once such type of laser gyroscope is known as a ring laser gyroscope. A ring laser gyroscope employs the Sagnac effect to measure rotation. That is that two counterpropagating light beams in a closed path will have transit times that differ in direct proportion to the rotation rate about an axis perpendicular to the plane of the path. In a ring laser gyroscope the closed path is defined by mirrors that direct the light beams around the path. The mirrors are precisely aligned to direct the light beams around the closed path. The mirror surfaces need to be free of defects to provide a laser beam intensity that will result in a usable signal.
As a result, the closed path is typically in a cavity formed in a frame or body that is formed of a glass ceramic material. The preferred glass ceramic material has a near zero coefficient of thermal expansion over the operating temperature range of a ring laser gyroscope. The glass ceramic preferred for ring laser applications is formed of a lithium alumino-silicate (LAS) material. The cavity is evacuated and then filled with a mixture of helium and neon, which is the gain medium for the laser. To excite the ring laser to cause two laser paths in opposite directions, it is customary to attach at least one cathode somewhere to the laser frame and to provide anodes on the laser frame together with conduits connecting the anodes and the cathodes into the laser bores in a geometric configuration, whereby a motion of ions and electrons between the cathode and anodes excites the laser phenomenon.
Application of a voltage of sufficient magnitude to ionize the gas between the cathode and anodes is applied to the cathode and to the anodes to cause a migration of electrons from the cathode to the anode and a migration of positive ions from the anodes to the cathode within the gain bores of the lasing gas, thereby exciting the lasing gas and producing counterpropagating light beams. The light beams are directed along the closed path by the precisely aligned mirrors, and captured by a detector outside the closed path. A rotation rate can be determined based on a comparison of the frequencies of the two counterpropagating light beams.